CRT is a treatment method for asynchronous cardiac motion. There is a need to set the position of the lead at a portion exhibiting asynchrony most noticeably. In this case, the positions of the great cardiac vein and anterior vein serve as landmarks.
The evaluation of asynchrony includes parametric imaging (a polar coordinate distribution, also called a polar map) based on wall motion tracking (cardiac wall tracking). This technique can identify a delayed region but does not provide a clear positional relationship with the above veins.
The above wall motion tracking allows to calculate a motor function index (motion index) of the cardiac wall, e.g., the change rate of cardiac wall thickness, for each minute section of a cardiac phase or in the interval between an end diastole (ED) and an end systole (ES), at multiple points throughout the heart. Note however that the heart is vertically long from the apex portion to the base portion. A polar coordinate distribution generally called a polar map is often generated as a display form of motion indices to allow to observe, at a glance, the motion indices of the overall heart which is vertically long. As is known, an expression method using polar coordinates is a method of expressing a plane by (r, θ) wherein θ represents an angle around the cardiac axis, and r represents a slice number assigned to each short-axis image of the region from the apex portion to the base portion.
This technique also segments a polar coordinate distribution into a plurality of segments in the radial and circumferential directions, calculates the average value of motion indices for each segment, and displays segment frames in color with hues corresponding to the average values. The technique also generates a temporal change in the average value of motion indices for each segment, and simultaneously displays the temporal changes. The polar coordinate distribution is segmented into segments uniformly in the circumferential direction regardless of the cardiac tissue. Average values vary depending on the range of cardiac tissue covered by each segment. For this reason, the reliability of temporal changes in the average value of motion indices are not very high.
For the above reasons, the utility value of a polar coordinate distribution associated with the motor function indices of the cardiac wall is not very high.